Golf balls of various structures have been proposed, such as one-piece golf balls which consist of a golf ball body; two-piece golf balls which include a core and a cover; three-piece golf balls which include a core having a center and a single intermediate layer covering the center, and a cover covering the core; and multi-piece golf balls which include a core having a center and two or more intermediate layers covering the center, and a cover covering the core.
Ionomer resins are widely used as a material for golf balls because such resins enable to produce golf balls which have high rigidity and fly a long distance. In particular, highly resilient materials are desired for golf balls. Ionomer resins having a higher degree of neutralization are known to achieve higher resilience but tend to simultaneously increase hardness, thus reducing flexibility and deteriorating shot feeling.
In consideration of the above problem, proposed is a method of reducing hardness while enhancing resilience by adding a large amount of fatty acid (metallic soap) to a highly neutralized ionomer resin. However, unfortunately, the acid component of the fatty acid consumes metal ions used for neutralization, thus preventing the highly neutralized resin from sufficiently providing a resilience-enhancing effect. Therefore, the method cannot sufficiently enhance flexibility and resilience in terms of producing golf balls satisfactory both in shot feeling and resilience. In addition, the method requires a large amount of metal component.
For example, Patent Literature 1 discloses a resin composition for golf balls providing excellent resilience and flexibility by adding a compound containing a hydrocarbon chain, a cationic moiety, and an anionic moiety in its molecule, such as oleyl betaine. However, this resin composition exhibits lower fluidity, thereby resulting in a reduction in productivity and processability. Accordingly, there is a need in the art for resin compositions for golf balls that simultaneously have excellent resilience, flexibility, and processability (fluidity).